i need help!

hi
im having this problem with my imac and i dono whats wrong with it.

when i delete a folder on a desktop the shadow of it stays there and it wont go you cant see it much but if u look really hard u can see the shadow of the file even thou its been deleted already its still there and also in welcome screen i have noticed few lines in the blue page!! and the lines are not just on the start up screen its on the desktop itself really really light lines, that u can barley see but u know its not normal when u see it across ur screen
dose anyone know whats wrong with it?

MacRumors attracts a broad audience
of both consumers and professionals interested in
the latest technologies and products. We also boast an active community focused on
purchasing decisions and technical aspects of the iPhone, iPod, iPad, and Mac platforms.